The majority of drugs currently used for advanced NSCLC induce cell cycle alterations and apoptosis. Apoptosis induction by these drugs appears dependent upon the E2F1 pathway. Specifically, we find these drugs induce E2F1 at the protein level and that E2F1 deficiency protects NSCLC cells from death induced by such agents. However, we have identified SirT1 as a novel negative regular of E2F1 that restricts E2F1-mediated induction of apoptosis by cytotoxic agents in a negative feedback loop. Preliminary data suggest that interference of this negative feedback significantly increases the sensitivity of NSCLC lines to drug-induced apoptosis. These results suggest the hypothesis that the E2F1/SirT1 pathway is crucial for efficacy of chemotherapeutic agents in NSCLC and provide proof-ofprinciple that targeting the E2F1/SirT1 pathway will have therapeutic benefit. This project will address three specific aims. Thus far results suggest that E2F1 activates SirT1 and that SirT1, in turn, limits E2F1-induced cell death. Preliminary data also would suggest that the E2F1/E2F4 ratio may play an important role in drug-induce apoptosis. However, we do fully understand whether other E2F family members play any significant roles in this process. Thus, the first specific aim will define the molecular interactions between SirT1 and members of the E2F family in NSCLC and will define the roles of different E2F family members in drug-induced apoptosis. This first aim will primarily address experimentation in tissue culture using NSCLC lines. The second specific aim will determine the contribution of the E2F1-SirT1 pathway to clinical outcome and therapeutic efficacy in lung cancer patients in ongoing clinical studies administered by the Thoracic Oncology Program. The purpose of this aim will be to understand whether the pathway that we have define in cell culture are applicable to the patient and whether E2F1, E2F4 or SirT1 will serve a prognostic markers in NSCLC. The third specific aim will seek to generate and characterize reagents that will disrupt the E2F/SirT1 pathway and define the functional consequences of this disruption in NSCLC chemotherapeutic interventions. We hypothesize that these agents will result in increased apoptosis in response to chemotherapeutic drugs and could ultimately have significant therapeutic value in NSCLC. The drugs used in the treatment of lung cancer could be highly effective;however, lung cancer cells have mechanisms that allow them to avoid death induced by these drugs. This project has discovered a new way cancer cells avoid death and proposes several ways to counterattack this process.